1. Field of the Invention
The present invention concerns a high-current coaxial conductor with two plug elements that can be connected with one another, in particular to connect a current-carrying coaxial conductor to a gradient coil of a magnetic resonance apparatus.
2. Description of the Prior Art
In magnetic resonance apparatuses an examination subject is exposed to a strong magnetic field to generate image exposures. This leads to an alignment of the nuclear spins of the atoms located in the magnetic field. The measurement signal for the imaging is obtained by the excitation of oscillations with radio-frequency energy. In order to obtain a spatial coding of the signals, magnetic gradient fields are used that are generated along the spatial directions with the use of gradient coils. The coils for the individual spatial directions are combined into a gradient coil system that has multiple individual coils respectively associated with the three spatial directions, and often also designated as a “gradient coil” for short. This gradient coil is spatially fixed in a casting compound in which it is sealed.
A high current must be supplied to the gradient coil to generate the gradient fields. The currents are several hundred amperes; for instance, currents of 500-900 A are typical.
Since no suitable high-current coaxial connection for connection of such a gradient coil has previously been available, it has been typical to split the coaxial line into two individual conductors before the connection to the coil, these two individual conductors then in turn being screwed down on the coil. The high current that must be supplied to the gradient coil therefore no longer flows coaxially in the connection region. Large alternating forces therefore occur in the stray field of the magnet, and therefore lead to a high, dynamic material strain due to the individual conductors. This entails the danger of a fracture or a loosening of the contact, which can cause a fire to start due to the large amount of energy at the gradient power amplifier (GPA).
In light of these problems, attempts have been made to produce the connection of the gradient coil by means of a high-current coaxial connection formed of two plug elements, namely a plug and a mating connector that can be detachably connected With the plug. The plug is located at the high-current coaxial conductor to be connected while the mating connector (thus the socket) is typically provided at the gradient coil (is permanently molded there). To connect, the plug is inserted into the mating connector. Both are naturally constructed so as to handle the high currents, namely the coaxial plug contacts are of approximate heavy-duty design and are insulated from one another. To hold the conductor-side plug to the coil-side mating connector, a coupling ring is provided that is screwed onto the mating connector. In principle, the possibility exists to realize a coaxial connection with such a high-current coaxial connection. Problems exist, in operation, however, because an unintended detachment of the plug connection can occur—due to mechanical vibrations and/or alternating electromagnetic forces at the individual plug elements or at the conductor-side plug contact—due to the coupling ring becoming detached due to the stresses (thus the fixed, threaded joint releases).